An HLA generally comprises a plunger slidably disposed within a cup-shaped body for fixed mounting in an internal combustion engine, which plunger may be hydraulically extended from the body to take up mechanical lash in an engine valve train. The HLA is supplied with low-pressure engine oil for conventional lubrication and for lash adjustment. A spring in a high-pressure chamber formed between the plunger and the body urges the plunger out of the body to take up mechanical lash in the valve train, thereby expanding the high-pressure chamber. A ball check valve between the low-pressure reservoir and the high-pressure chamber allows that chamber to fill with oil, thereby making the HLA hydraulically rigid. As oil escapes from the high-pressure chamber by leakage around the plunger, the lost oil is replenished through the check valve. If the effective length of the valve train shortens during the engine's cam operating cycle, positive lash is created and the HLA extends, moving the plunger to a higher position at the end of the cycle than at the beginning. Inversely, if the effective length of the valve train lengthens during the cam cycle, negative lash is created and the lash adjuster contracts, moving the plunger to a lower position at the end of the cycle than at the beginning. The latter condition typically occurs when valve train components lengthen in response to increased temperature.
A problem exists in some prior art HLA assemblies. A prior art one-piece plunger has a ball surface at its outer end with a central opening for supplying oil from the low-pressure reservoir to the socket end of an associated rocker arm assembly, the reservoir being supplied via a radial port in a sidewall of the reservoir. The inner end of the plunger comprises a seat for the check valve. See, for example, FIG. 2 in U.S. Pat. No. 5,642,694. Included below the seat as separate items are the check valve and return spring, valve cage and plunger spring.
It is more common in the art to provide an HLA plunger formed as two shorter sections—a lower section and an upper section. See, for example, FIG. 1 in U.S. Pat. No. 5,622,147. In this example, the seat for the check valve is integrally formed in the lower section of the plunger. Below the seat, as separate items, are the check valve and return spring, valve cage and plunger spring.
In the co-pending application bearing Ser. No. 10/897,885, an HLA assembly having a one piece tubular plunger is shown. A separate seat element is fitted to the plunger after the plunger is formed thereby simplifying the manufacture of the tubular plunger. Similar to the other prior art examples, the check valve and valve cage are assembled as separate pieces below the seat element.
It is a principal object of the present invention to provide a hydraulic lash adjuster including a plunger that is easier to manufacture wherein the check valve assembly is provided as a cartridge sub-assembly.